Migration: Generate the completed event only when we complete

Migration: Generate the completed event only when we complete

The current migration-completed event is generated a bit too early,
which means that an eager libvirt that's ready to go as soon
as it sees the event ends up racing with the actual end of migration.

This corresponds to RH bug:
https://bugzilla.redhat.com/show_bug.cgi?id=1271145

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Reviewed-by: Amit Shah <amit.shah@redhat.com>
xSigned-off-by: Juan Quintela <quintela@redhat.com>
(cherry picked from commit ed1f3e0090069dcb9458aa9e450df12bf8eba0b0)
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>